1. Field of the Invention
The present invention relates to an overcurrent monitoring system for use with an electrical motor and, in particular, a system for determining press operating conditions based on the electrical load on an electrical press drive motor used in a machine press.
2. Description of the Related Art
As a machine press operates, there are variations in the electrical load drawn or created by the press motor. If the current load on the motor exceeds the motor's capacity, damage and loss of use may ensue. For example, current overload may cause burnout to the motor and associated portions such as the bearings, bushings, or commutators.
Load variations may be attributed to normal press operational functions. Alternatively, load variations may not be the result of normal press functions. For effective protection, it is essential to detect normal press functions which effect electrical load.
Normal press operations that effect the electrical load include initial starting of the press drive motor, engaging the press clutch, and varying the press operating speed. Other changes which effect the electrical load include lubricating oil temperature changes and die changes.
If the electrical load increase is not attributed to normal press operations, the current increase could be an indication of a potential problem in press operation. For example, when bearings or bushings overheat, the press speed tends to slow down and there is an increase in press motor drive load. Therefore, an increase in the electrical load may indicate that press bushings or bearings are overheating. In order to safeguard the press, it is advantageous to cut power to the motor when an increase in current load is not attributed to a normal press function to permit service personnel to determine the actual cause of the increased motor load.
In the art, monitoring systems have been limited to monitoring the effective power consumption of the press motor. In addition, such motor monitoring is not constant; rather, the monitoring is limited to only a portion of the press stroke.
It is advantageous to account for variations in motor electrical current draw attributed to normal press operations. Such detection would make it possible to stop the drive motor and press before potential damage may be caused to the motor, press bearings and bushings. In turn, there is a financial benefit in preventing damage to the machine press.
The present invention prevents potential damage to a machine press motor and press when the motor electrical current draw is above predetermined limits.